1. Field
This disclosure relates generally to circuits, and more specifically, to a drain-to-gate leakage protection circuit and method therefor.
2. Related Art
Very large MOS (metal-oxide semiconductor) transistors are used in high current applications. One application that requires a very large MOS transistor is a high-side switch used for driving a motor. Typically in a high-side switch, a drain of the MOS transistor is connected directly to a power supply voltage. When the circuit is turned off, such as during a low power operating mode, a gate-to-source voltage (VGS) of the MOS transistor is made to be zero to minimize a drain-to-source sub-threshold leakage current. However, a defect in the dielectric layer between the gate and drain may cause a leakage current from the drain to the gate of the MOS transistor even when the transistor is off. The leakage current can increase the VGS so that the MOS transistor is operating in a linear operating region when the transistor is intended to be off. Because of the large transistor size, the leakage current can be in the milliamp range. Over time, the temperature of the transistor may increase until a thermal event occurs, resulting in damage to the device. To ensure that the off transistor's VGS does not increase in the case of a gate-to-drain defect, a resistor may be connected between the gate and source to ensure the transistor's VGS is substantially zero. However, if the resistance value is too high, the resistor will be ineffective for pulling the gate voltage down. If the resistance value is too low, the transistor will be prevented from operating properly during a normal operating mode.
Therefore, what is needed is a circuit that solves the above problems.